Transmembrane currents play a fundamental role in the activation and functioning of excitable tissues. In urinary bladder smooth muscle, depolarization, excitation-contraction, and repolarization are dependent upon the activation of transmembrane currents through voltage dependent ion channels. The current underlying repolarization in detrusor smooth muscle is carried through several ion channels, virtually all of which utilize potassium as the charge carrier. Several of these channels have been the target of compounds and drugs aimed at modulating the physiology and functioning of smooth muscle and other tissues [Edwards, G & Weston, A H, “Pharmacology of the potassium channel openers”, Cardiovasc Drugs Ther 9 (Suppl. 2): 185-193 (1995), which is incorporated herein by reference in its entirety].
It has been suggested that a potassium channel opener (KCO) may be useful in the treatment of detrusor hyperactivity [Foster D C & Brading A F, “The effect of potassium channel antagonists on the BRL 34915 activated potassium channel in guinea-pig bladder”, Br J Pharmacol 92: 751 (1987), which is incorporated herein by reference of in its entirety]. An increase in potassium channel permeability would hyperpolarize the cell, bring the membrane potential further from the threshold for activation of calcium channels and reduce excitability [Brading A F, “Ion channels and control of contractile activity in urinary bladder smooth muscle”, JPN J Pharmacol 58 (Suppl 2): 120P-127P (1992), which is incorporated herein by reference in its entirety]. A number of potassium channel openers have shown activity in isolated tissues [Malmgren A, et al., “Effects of cromakalim (BRL 34915) and pinacidil on normal and hypertrophied rat detrusor in vitro”, J Urol 143: 828-834 (1990); Grant T L & Zuzack J S., “Effects of K+ channel blockers and cromakalim (BRL 34915) on the mechanical activity of guinea pig detrusor smooth muscle”, J Pharmacol Exp Ther 269(3): 1158-1164 (1991), each of which is incorporated herein by reference in its entirety] and efficacy in both experimental and clinical bladder instability [Foster & Brading, supra, Br J Pharmacol 92: 751 (1987); Malmgren A, et al., “Effects of pinacidil and cromakalim (BRL 34915) on bladder function in rats with detrusor instability”, J Urol 142: 1134-1138 (1989); Wojdan A, et al., “Comparison of the potassium channel openers ZD6169, celikalim and WAY-133537 on isolated bladder tissue and in vivo bladder instability in the rat”, J Pharmacol Exp Ther 289(3): 1410-1418 (1999), each of which is incorporated by reference in its entirety). However, because these compounds also activate channels in vascular smooth muscle, causing vasodilation, the clinical utility has been severely limited by hemodynamic side effects including hypotension and tachycardia.
It has been stated previously that retigabine (N-[2-amino-4-(4-fluorobenzylamino)-phenyl]carbamic acid ethyl ester) activates a member of the KCNQ family of potassium channel in the bladder which is most likely KCNQ2/3 and/or KCNQ3/5 [Wickenden A D, et al., “Retigabine, a novel anti-convulsant, enhances activation of KCNQ2/Q3 potassium channels”, Molec Pharmacol 58: 591-600 (2000); Wickenden, A D, et al., “Characterization of the KCNQ5/Q3 potassium channels expressed in mammalian cells”, Br J Pharmacol 132(2): 381-384 (2001); Rundfeldt, C & Netzer, R, “The novel anticonvulsant retigabine activates M-currents in Chinese hamster ovary-cells tranfected with human KCNQ2/3 subunits”, Neurosci Lett 282(1-2): 73-76 (2000); Main, M J, et al., “Modulation of KCNQ2/3 potassium channels by the novel anticonvulsant retigabine”, Mol Pharmacol 58(2): 253-262 (2000), each of which is incorporated herein by reference in its entirety]. The result is an inhibition of bladder smooth muscle contractility. In addition, recent data provides evidence for the existence of the KCNQ4 channel in human bladder smooth muscle. Current knowledge of KCNQ4 suggests that it may form a functional ion channel on its own [Sogaard, R, et al., “KCNQ4 channels expressed in mammalian cells: functional characteristics and pharmacology”, Am J Physiol Cell Physiol 280(4): C859-C866 (2001), which is incorporated herein by reference in its entirety], or that it may combine with KCNQ3 [Kubisch C, et al., “KCNQ4, a novel potassium channel expressed in sensory outer hair cells, is mutated in dominant deafness”, Cell 96(3):437-446 (1999), which is incorporated herein by reference in its entirety]. It is likely therefore, that retigabine's effects on bladder smooth muscle include activation of the KCNQ4 channel in addition to the channels formed by KCNQ2/3 and KCNQ3/5. Activation of this channel will hyperpolarize the bladder smooth muscle cells and, in doing so, relax the bladder. Since these KCNQ channels are not present in the cardiovascular system, retigabine and other molecules that activate these channels should be useful in the treatment of bladder instability without hemodynamic compromise.
M-currents have been shown to play an important functional role as determinants of cell excitability. Recent evidence indicates that the KCNQ potassium channel subunit form the molecular basis for M-current activity in a variety of tissues. From their initial report in peripheral sympathetic neurons the gene family has evolved to contain at least five major sub-units designated KCNQ1 though KCNQ5 [Rogowski, M A, “KCNQ2/KCNQ3 K+ channels and the molecular pathogenesis of epilepsy: implications for therapy”, Trends Neurosci 23: 393-398, (2000); Jentsch, T J, “Neuronal KCNQ potassium channels: physiology and role in disease”, Nat Rev Neurosci 1(1):21-30 (2000), each of which is incorporated herein by reference in its entirety]. These sub-units have been shown to co-assemble to form both heteromeric and homomeric functional ion channels. Recent reports indicate that both KCNQ2 and KCNQ5 can co-assemble with KCNQ3 [Tinel, N, et al., “The KCNQ2 potassium channel: splice variants, functional and developmental expression. Brain localization and comparison with KCNQ3”, FEBS Lett 438(3): 171-176 (1998); Yang, W P, et al., “Functional expression of two KvLQT1-related potassium channels responsible for an inherited idiopathic epilepsy”, J Biol Chem 273(31):19419-19423 (1998); Wang, H S, et al., “KCNQ2 and KCNQ3 potassium channel subunits: molecular correlets of the M-channel”, Science 282(5395): 1890-1893 (1998); Lerche, C, et al., “Molecular cloning and functional expression of KCNQ5, a potassium channel subunit that may contribute to neuronal M-current diversity”, J Biol Chem 275(29): 22395-22400 (2000); Schroeder, B C, et al., “KCNQ5, a novel potassium channel broadly expressed in brain, mediates M-type currents,” J Biol Chem 275(31): 24089-24095 (2000), each of which is incorporated herein by reference in its entirety] to form a functional M-channel activatable by retigabine [Wickenden, supra, Molec Pharmacol 58: 591-600 (2000); Wickenden, supra, Br J Pharmacol 132(2): 381-384 (2001); Rundfeldt & Netzer, supra, Neurosci Lett 282(1-2): 73-76 (2000); Main, supra, Mol Pharmacol 58(2): 253-262 (2000)] and blocked by either acetylcholine [Adams, P R, et al., “M-currents and other potassium currents in bullfrog sympathetic neurones”, J Physiol 330: 537-72 (1982); Brown, D A & Adams, P R “Muscarinic suppression of a novel voltage-sensitive K+ current in a vertebrate neurone”, Nature 283: 673-676 (1980); Shapiro, M S, et al., “Reconstitution of muscarinic modulation of the KCNQ2/KCNQ3 K(+) channels that underlie the neuronal M current”, J Neurosci 20(5): 1710-1721 (2000), each of which is incorporated herein by reference in its entirety], linopirdine, or XE-991 (10,10-bis(4-pyridinylmethyl)-9(10H)-anthra-cenone) [Aiken, S P, et al., “Reduction of spike frequency adaptation and blockade of M-current in rat CA1 pyramidal neurons by linopirdine (DuP 996) a neurotransmitter release enhancer”, Br J Pharmacol 115(7): 1163-1168, (1995); Zaczek R, “Two new potent neurotransmitter release enhancers, 10,10-bis(4-pyridinylmethyl)-9(10H)-anthracenone and 10,10-bis(2-fluoro-4-pyridinylmethyl)-9(10H)-anthracenone: comparison to linopirdine”, J Pharmacol Exp Ther 285(2): 724-730 (1998), each of which is incorporated herein by reference in its entirety]. The parasympathetic neurotransmitter acetylcholine (Ach) is known to produce several physiological responses in bladder smooth muscle. The net result of Ach exposure is a contraction of the smooth muscle mainly through the mobilization of transmembrane and intracellular calcium stores [Hashitani H, et al., “Mechanisms of excitatory neuromuscular transmission in the guinea-pig urinary bladder”, J Physiol 524(Part 2): 565-579 (2000), which is incorporated herein by reference in its entirety]. The role that Ach plays in modulating the cell transmembrane potential, however, is more complex. Pathways for both hyperpolarization and depolarization are present with muscarinic stimulation of bladder smooth muscle. Hyperpolarization may be associated with a mechanism that involves calcium sparks and activation of calcium-dependent potassium currents [Herrera G M, et al., “Voltage dependence of the coupling of Ca(2+) sparks to BK(Ca) channels in urinary bladder smooth muscle”, Am J Physiol Cell Physiol 280(3): C481-490 (2001), which is incorporated herein by reference in its entirety].
Given their potential in the treatment of urinary incontinence and other disorders, there is an interest in developing new potassium channel modulators. This invention addresses these needs and others.